1. Field of the Invention
The present invention relates to an impression forming mechanism and an impression forming method which are employed in a testing apparatus that evaluates a material characteristics of a sample by applying a force to a surface of the sample with an indentor in order to from an impression thereon, and a hardness testing apparatus comprising the impression forming mechanism and method. The present invention also relates to a hardness testing apparatus and a hardness testing method, having an electromagnetic brake.
2. Description of the Related Art
In the related art, a hardness testing apparatus is known as a testing apparatus that evaluates the material characteristics of a sample based on an impression formed by applying a force (or load) to a surface of the sample with an indentor.
As a force applying mechanism in the hardness testing apparatus in the related art, for example, a mechanism shown in FIG. 13 is known.
A hardness testing apparatus 100 as shown in FIG. 13 is the so-called Rockwell type hardness testing machine. The hardness testing apparatus 100 has an impression forming mechanism 110 comprising weights 101, a loading arm 102, a cam 103, a force shaft 104, an indentor shaft 105, an indentor 106, etc, and a sample table 107.
In the impression forming mechanism 110, the weights 101 having a predetermined weight are hung from an end of the loading arm 102. The end of the loading arm 102 moves down by the rotation of the cam 103, and then a predetermined force (or load) is applied to the force shaft 104. The force applied to the force shaft 104 is transmitted to the indentor 106 via the indentor shaft 105. Thus, an impression is formed on a sample mounted on the sample table 107, by a downward movement of the indentor 106.
In a force applying control by using the weights, which is employed typically in the above hardness testing apparatus 100, there is a problem that it cannot be confirmed whether the force having a set value is applied to the sample while an impression is formed on the surface of the sample.
Also, since the force is applied to the sample by using the weights, the force that exceeds a target force, i.e., the so-called overshoot, is generated unless a speed for applying the force to the sample is slowed down by a damper, or the like. There is also a problem that, even if the damper is employed, it is difficult to eliminate the small overshoot.
In order to overcome the problems, there is a method that the force is applied to the sample by executing electrically the force applying control. In the case of the electrical force applying control, the loading arm having a high rigidity is employed for the convenience of control.
Further, an electromagnetic brake is employed for stopping the sample table once when the sample is brought into contact with the indentor in order to apply a preliminary test force to the surface of the sample.
The electromagnetic brake uses an electromagnet that is arranged under the sample table, and if a predetermined force is applied to the indentor when the sample is brought into contact with the indentor, a current is passed through the electromagnet so that a brake is applied to an elevating operation of the sample table. With the electromagnetic brake, an operation of applying the force to the sample can be carried out precisely.
However, in the hardness testing apparatus having the loading arm with the high rigidity, an impact (stepwise force) is easily applied to the sample at an instant when the sample and the indentor are brought into contact with each other manually. In some cases, a force that excesses the preliminary test force is easily applied to the sample at an instant when the sample and the indentor are brought into contact with each other manually.
In such case, there is a problem that the hardness testing apparatus cannot be carried out preciously.
Further, for the sample table, a high mechanical strength and a high rigidity are required, and thus a magnetic substance such as iron, or the like is used as the material for the sample table. Accordingly, due to the use of the electromagnet of the electromagnetic brake, the sample table is magnetized and also the sample mounted on the sample table is magnetized.
Such magnetization is at the level that the measuring precision of the hardness testing apparatus is not influenced. However, in the test of the sample, such as a thin sample, a lightweight sample, or the like, which is easy to be attracted to the magnet, the sample is attracted to the electromagnet and pasted onto the sample table, whereby a replacing operation of the sample becomes troublesome.
The present invention has been made to overcome the above problems. In is a first object of the present invention is to provide an impression forming mechanism and an impression forming method and a hardness testing apparatus, having a loading arm with high rigidity, which can reduce an impact generated at an instant when an indentor and a sample are brought into contact with each other and also apply an preliminary test force to the sample easily and precisely.
Further, it is a second object of the present invention to provide a hardness testing apparatus and a hardness testing method, having an electromagnetic brake, which can test a thin sample, etc. effectively and also can test a sample, in which a problem is caused if the sample is magnetized.
In order to accomplish the first object above, the following means are adopted. According to a first aspect of the present invention, there is provided an impression forming mechanism for forming an impression on a surface of a sample with an indentor, comprising:
an impact reducing unit for controlling a movement of one of the sample and the indentor in a same direction as the other of the sample and the indentor when the sample comes close to the indentor and a distance between the sample and the indentor is within a predetermined distance.
According to the impression forming mechanism of the first aspect of the present invention, since the impact reducing unit is provided, the impulse that is applied to the sample by the indentor at an instant when the sample comes into contact with the indentor can be reduced. In other words, since the impact generated at an instant when the sample comes into contact with the indentor can be reduced, it is possible to overcome the problem such that the force exceeds a preliminary test force at an instant of contact.
In the impression forming mechanism of a second aspect of the present invention, according to the first aspect of the present invention, it is preferable that the impact reducing unit controls the movement of one of the sample and the indentor in a same direction as the other when the sample comes into contact with the indentor, the impact reducing unit including,
a force controlling unit for calculating a predetermined force which is to be applied to the sample, in response to a displacement from a reference position of the indentor when the sample comes into contact with the indentor, and
a moving unit for moving the indentor in a same direction as the sample such that the predetermined force calculated by the force controlling unit is applied to the sample.
According to the impression forming mechanism of the second aspect of the present invention, since the force controlling unit and the moving unit are provided, the force can be applied to the sample in response to the displacement from the reference position of the indentor. Thus, the operator who moves the sample manually can apply the predetermined force to the sample more appropriately by operating only the handle, etc. in the same manner as the related art.
In the impression forming mechanism of a third aspect of the present invention, according to the first or second aspect of the present invention, it is preferable that the impact reducing unit further includes a distance sensing unit for sensing the distance between the indentor and the sample, and the impact reducing unit controls the movement of one of the sample and the indentor in a same direction as the other at a predetermined speed when the sample comes close to the indentor.
According to the impression forming mechanism of the third aspect of the present invention, since the distance sensing unit is provided, the one of the sample and the indentor can be moved in the same direction as the other immediately before the sample is brought into contact with the indentor. Thus, the impact can be reduced further more at an instant when the sample comes into contact with the indentor.
Further, in order to accomplish the first object above, there is provided a hardness testing apparatus according to a fourth aspect of the present invention, which comprises the impression forming mechanism according to the first, second, or third aspect of the present invention.
According to the hardness testing apparatus of the fourth aspect of the present invention, since the impression forming mechanism of the first, second, or third aspect of the present invention is provided, the sample and the indentor can be contacted mutually such that the force does not easily exceed the preliminary test force at an instant when the sample comes into contact with the indentor, and therefore the working efficiency can be improved. Also, since the force never exceeds the preliminary test force at an instant of contact, the reliability of the result about the hardness testing apparatus can be improved.
In order to accomplish the second object above, the following means are adopted. According to a fifth aspect of the present invention, there is provided a hardness testing apparatus comprising:
a sample table for mounting a sample thereon;
an electromagnetic brake for controlling an elevating operation of the sample table; and
a current supplying unit for supplying a current to the electromagnetic brake and inverting a direction of the current supplied to the electromagnetic brake at a predetermined timing.
According to the hardness testing apparatus of fifth aspect of the present invention, since the direction of the current that flows through the electromagnetic brake is inverted at a predetermined timing by the current supplying unit, a magnetic force having the opposite direction is supplied to the sample table, which is magnetized by the drive of the electromagnetic brake, to demagnetize the magnetization of the sample table. Therefore, the sample that is easily attracted by the magnet such as the thin sample, or the like is prevented from being pasted onto the sample table, and the replace of the sample can be conducted effectively.
Here, xe2x80x9cimmediately after the electromagnetic brake is appliedxe2x80x9d or xe2x80x9cbefore the sample is exchangedxe2x80x9d may be selected as the xe2x80x9cpredetermined timingxe2x80x9d. Also, only in the test in which the problem is caused if the sample is magnetized, the current may be inverted manually, or any timing may be given manually.
In the hardness testing apparatus of a sixth aspect of the present invention, according to the fifth aspect of the present invention, it is preferable that the current supplying unit supplies a driving current to drive the electromagnetic brake and then supplies a current, which has an opposite direction to the driving current, in a shorter time than the driving current.
According to the hardness testing apparatus of the sixth aspect of the present invention, after the driving current for driving the electromagnetic brake is supplied by the current supplying unit, the current having the direction opposite to the driving current is supplied in a period that is shorter than that of the driving current. Therefore, the magnetization of the sample table in the opposite direction by supplying the current in the same current supply time as that of the driving current or in the longer time than that of the driving current can be prevented. Thus, the sample table that is magnetized by the drive of the electromagnetic brake can be demagnetized, the sample that is easily attracted by the magnet such as the thin sample, or the like is hard to be pasted onto the sample table, the exchange of the sample can be conducted effectively. Further, the test of the sample, in which the problem is caused if such sample is magnetized can be accomplished.
Here, like the above current supplying unit, the current, the current supply time of which is shorter than the preceding current and which has the direction opposite to that of the preceding current, may be supplied plural times. If doing this, the magnetic force of the sample table can be demagnetized gradually and also the larger demagnetization effect can be achieved.
In the hardness testing apparatus of a seventh aspect of the present invention, according to the sixth aspect of the present invention, it is preferable that the current supplying unit supplies the driving current to the electromagnetic brake in an opposite direction of the prior driving current, which was supplied to the electromagnetic brake, every time when the electromagnetic brake is driven.
According to the hardness testing apparatus of the seventh aspect of the present invention, the current is supplied by the current supplying unit while inverting the direction of the current, which is supplied to the electromagnetic brake, every time when the electromagnetic brake is driven. Therefore, since the currents in the positive and negative directions can be supplied uniformly to the electromagnetic brake, the magnetization of the sample table by the electromagnetic brake is never deviated in one direction, and the demagnetization effect can be obtained much more. The exchange of the sample that is easily attracted by the magnet becomes easy at the time of replace. Further, the test of the sample, in which the problem is caused if such sample is magnetized, can be accomplished.
In order to accomplish the second object above, there is provided a harness testing apparatus comprising:
a sample table for mounting a sample thereon;
an electromagnetic brake for controlling an elevating operation of the sample table; and
a high-frequency voltage applying unit for applying a high-frequency voltage to the electromagnetic brake in order to demagnetize the sample table that is magnetized by the electromagnetic brake.
According to the hardness testing apparatus of the eighth aspect of the present invention, there is provided the high-frequency voltage applying unit for applying the high-frequency voltage to the electromagnetic brake to demagnetize the sample table that is magnetized by the drive of the electromagnetic brake. Therefore, the magnetic force of the sample table can be eliminated by the AC demagnetization, the exchange of the sample that is easily attracted by the magnet becomes easy at the time of replace. Thus, not only the test can be conducted effectively but also the test of the sample, in which the problem is caused if such sample is magnetized, can be accomplished.